Abstract : Biomass flowability is a major issue in the processes dedicated to the thermochemical conversion of biomass based on technologies such as downward-moving bed reactor, dense fluidized bed reactor and entrained flow gasifier. Torrefaction is an example of process influencing powder mechanical property: researchers [1] recently proved torrefaction changes the physical and chemical properties of the material. In particular, it improves the feedstocks homogenization and makes the grinding easier. In the field of this biomass pretreatment for biofuel production, IFP Energies nouvelles and Ecole des Mines de Saint-Etienne study the effects of the combined torrefaction and grinding processes. An experimental protocol then was developed to observe (i) the major particle behavior: anhydrous weight loss (AWL), grindability, particle size and shape, surface state, (ii) and the major powder behavior: bulk density, flowability, compressibility, aerability. One parameter is studied there, the torrefaction temperature. To perform the particles and powders characterization, several techniques were used: optical microscopy, scanning electron microscopy, Flodex® methodology and powder rheometer. Samples of spruce are first torrefied at different temperatures (S240, S300) then ground with a sieving grid of 0.5 mm. From 200 to 300°C, the AWL increases from 1 to 26%. The rheological study of the biomass powders shows that flowability is significantly improved in the only case of a high torrefaction (S300). Compressibility and aerability are also increased with the level of torrefaction temperature. These results are correlated to particles morphological characterization: the powder rheological behavior is only influenced by a characteristic size parameter, such as Sauter mean diameter.